This invention relates to a terminal crimping apparatus for crimping a metal terminal (having a pair of crimping piece portions (barrel) extending upwardly respectively from opposite side edges of a base plate portion thereof) to a core wire of an electric wire.
There is known one conventional terminal crimping apparatus for crimping a terminal to a core wire of an electric wire, in which crimping piece portions of the terminal are pressed by an anvil and a crimper, and are press-fastened to the core wire (see, for example, JP-A-2002-373755 (FIG. 1)).
As shown in FIG. 7, the apparatus disclosed in JP-A-2002-373755 includes the anvil 4 for holding the metal terminal 6, and the crimper 3 located above the anvil 4 and having a pair of press-deforming portions 2 and 2 formed on a surface thereof facing the anvil 4. In this apparatus, a core wire 7 is placed on and received in the metal terminal 6 supported on the anvil 4, and in this condition the crimper 3 is moved downward, so that crimping piece portions 6a and 6a (jointly assuming a generally U-shaped cross-section) are pressed between the crimper 3 and the anvil 4, and are press-fastened to the core wire 7.
In recent years, with a compact design of electronic equipments, there have been proposed metal terminals for connection to a very thin electric wire including a core wire having a cross-sectional area of 0.08 to 0.13 mm2. In such very thin electric wires, a copper alloy harder than conventionally-used annealed copper and brass is used as a material for the core wire in view of a wire strength. However, the conventional crimping apparatus is not designed for such a thin, hard electric wire, and therefore when the metal terminal is crimped to the very thin electric wire with this conventional crimping apparatus, there is a fear that there may develop variations in the amount of biting of the crimping piece portions of the metal terminal and the height and width of a wire crimped portion of the metal terminal. And besides, when such variations develop, the crimped shape becomes unstable, which leads to a fear that a clamping force and an electrical performance may be lowered. Furthermore, in the case of the very thin electric wire, the connection performance is particularly adversely affected by the above variations.
Therefore, there has been proposed a terminal crimping method designed for a very thin electric wire (see, for example, JP-A-2006-49117 (FIGS. 3 and 4)). In the method disclosed in JP-A-2006-49117, dimensions of a metal terminal and dimensions (a height and a width of a crimped portion) of the crimped metal terminal are decreased according to the down-sizing of the electric wire, and the crimped terminal is produced, and by doing so, the optimum range is determined. And, in the case of a very thin electric wire including a high-strength core wire, the metal terminal is press-fastened without contact with the core wire, and by doing so, a sufficient tensile strength is secured even when the terminal is crimped to the core wire.
However, in the above conventional crimping technique for the very thin electric wire, when variations develop in the amount of biting of crimping piece portions of the metal terminal and the height (crimp height) and width (crimp width) of the crimped portion, the crimped shape becomes unstable, which leads to a fear that the clamping force and the electrical performance may be lowered.
When the metal terminal is crimped to the very thin electric wire, there develop the reduced contact area due to the increased crimp height caused by the overlapping of one crimping piece portion of the metal terminal on the other crimping piece portion, the reduced strength of the conductor due to the reduced crimp height caused by the bottoming of one crimping piece portion, etc. Therefore, there has been encountered a problem that the force (strength) of clamping of the metal terminal to the electric wire is lowered, so that the mechanical and electrical performances are lowered.